The applicability of transfer factor (TF) for colorectal carcinoma will be explored by an in depth study rather than a large scale clinical trial. A horizontal study will be performed on two groups of patients: 1) Post-op less than 3 years free of disease and 2) recurrent disease. The incidence and degree of "serum blocking factors" (SBF) according to stage, disease-free interval and tumor burden will be assessed utilizing the leukocyte adherence inhibition (LAI)-blocking assay. By random selection, TF from three sources - 1) "cured" colorectal carcinoma, 2) "cured" breast carcinoma and 3) normal control - will be administered to both groups of patients twice, 7 days apart, following which the effects of TF on LAI and SBF will be assessed. The unblocking effect of TF will be measured by an in vivo and in vitro assay technique. These studies could explain the mode of action of TF (? unblocking) and the specificity of TF. A vertical study will consist of investigation of patients undergoing curative resection of colorectal carcinoma. Pre- and postoperative serial LAI-blocking assays will be correlated with stage of disease, tumor burden and CEA. LAI-blocking assay may serve as a prognosticator and an adjunct to treatment of colorectal carcinoma.